1. Field of the Invention
The present invention generally relates to a drive control system of stepping motors used for feeding paper in facsimile devices, and more particularly is directed to a drive control system of stepping motors employed for performing micro-step driving.
2. Description of the Prior Art
Known stepping motor storing data tables store current values of current flowing in each phase of the motor. The data tables also store addresses for each current value. To read out a particular current value, the address corresponding to the particular current value is accessed. In recent years, for a more accurate driving of a stepping motor, a microstep driving system has been adopted in which the motor can be driven according to addresses for intervals between the phases of the motor.
FIG. 20 shows the data characteristics of the above-mentioned data tables when driving a 2-phase stepping motor. During the driving thereof, the current values of current flowing through the phases A and B of the motor are obtained from the sinusoidal waves of phases A and B shown in FIG. 20, which are 90 degrees out of phase with each other. Therefore, for the current value associated with each address in the table, a numerical value close to those indicated by these curve lines is selected to prepare the data table. The data table provides current values for a 1-cycle portion of the operation of the motor. The table is constructed such that the number of addresses from the address where the phase A current value is at its peak and the phase B current value is zero, to the address at which the current values of phase A and phase B become equal, is the same as the number of addresses from the address where current values of phases A and B become equal, to the address at which the phase A current value is zero and the B phase current value is at its peak. When driving the motor, table addresses are sequentially accessed and driving is achieved according to the read-out current values corresponding to the accessed addresses.
The drive response characteristics of such stepping motors, however, cause the rotation angles to not be uniform, when the addresses are sequentially accessed one by one, as shown in FIG. 20. Thus, there are rotation irregularities. In other words, at an address, C, intermediate between the address where the phase A current value becomes a peak and the address where the phase B current value becomes a peak, each motor displacement .alpha.', is not equal to another motor displacement .beta.'. In this instance, .alpha.' represents the displacement to C from the address where the phase A current value becomes a peak, while .beta.', denotes the displacement from C to the address where the phase B current value becomes a peak. Thus, rotation irregularities occur in motors rotated under such drive response characteristics, resulting in the generating of noise or vibration. Therefore, precision printing is not possible due to unequal rotation angles which occur during one-by-one sequential accessing of addresses, in spite of the fact that high-accuracy paper feeding is achieved by such microstep driving.
Further, the drive response characteristics of the motor which cause motor rotation irregularities vary, depending on the type of motor and the motor drive conditions, and can accompany different drive pulse rates, different load intensities, and other factors.
Switching between forward rotation and reverse rotation of motors is conventionally achieved by reversing the direction in which addresses are sequentially accessed in a table in which current values are set based on the sinusoidal wave ratios as shown in FIG. 20. Such a switching method was adopted because the drive response characteristics of the motor are symmetrical with respect to the forward and reverse rotational directions of the motor. When an excitation current having such characteristics is applied to each phase, the motor should demonstrate ideal forward and reverse directional rotation.
With actual drive systems, however, because of the effects of loads on motors, it is not possible to attain stable motor driving even when normal/reverse motor rotation is performed by using the identical tables.